Liquid crystal display panel and liquid crystal display device

ABSTRACT

The present invention provides a liquid crystal display panel and a liquid crystal display device having excellent display quality, with reduced string-like defects that occur in display pixels. The liquid crystal display panel of the present invention includes multiple spacers between a pair of substrates, wherein the spacers are arranged such that an inter-spacer distance between adjacent spacers in a longitudinal direction is different from an inter-spacer distance between adjacent spacers in a transverse direction, and an angle formed between a line connecting the spacers with a shorter inter-spacer distance and an alignment direction of liquid crystal molecules at a voltage lower than a threshold voltage in the liquid crystal layer is 20° or smaller.

TECHNICAL FIELD

The present invention relates to a liquid crystal display panel and aliquid crystal display device. More specifically, the present inventionrelates to a liquid crystal display panel and a liquid crystal displaydevice including a polymer layer for improving a property formed on ahorizontal photo-alignment film.

BACKGROUND ART

Due to advantageous features such as thin profile, light weight, and lowpower consumption, liquid crystal display devices are used in a widerange of fields including mobile communication systems, monitors, andlarge televisions. Various performances are required in these fields,and various display modes have been developed. As the fundamentalstructure and principle, these liquid crystal display devices include apair of substrates for interposing a liquid crystal layer therebetween;and control the transmission/shielding of light (on/off of the display)by appropriately applying a voltage to electrodes disposed on the liquidcrystal layer side of at least one of the pair of substrates, and bycontrolling the alignment direction of liquid crystal molecules in theliquid crystal layer, thus achieving liquid crystal displays.

Examples of the display modes of recent liquid crystal display devicesinclude a vertical alignment (VA) mode in which liquid crystal moleculeshaving negative anisotropy of dielectric constant are aligned verticallyto the substrate surface; and an in-plane switching (IPS) mode and afringe field switching (FFS) mode in which liquid crystal moleculeshaving positive or negative anisotropy of dielectric constant arealigned horizontally to the substrate surface, and a horizontal electricfield is applied to the liquid crystal layer.

Herein, as a method of obtaining a high-luminance and high-speedresponse liquid crystal display device, alignment stabilizationtechniques using a polymer (hereinafter, also referred to as “polymersustained (PS) treatment”) have been suggested (for example, see PatentLiteratures 1 to 9). Among these, according to pre-tilt angle impartingtechniques using a polymer (hereinafter, also referred to as “polymersustained alignment (PSA) technique”), polymerizable components such asa polymerizable monomer and a polymerizable oligomer are mixed to obtaina liquid crystal composition, which is then sealed between thesubstrates; a voltage is applied between the substrates to tilt liquidcrystal molecules; and the monomer is polymerized to form a polymer,with the liquid crystal molecules being tilted. This results in liquidcrystal molecules that are tilted at a certain pre-tilt angle even afterthe voltage application is stopped, and thus the liquid crystalmolecules can be aligned in a certain direction. Materials that arepolymerizable by heat, light (ultraviolet light), and the like areselected as monomers to form a polymer.

According to another disclosed document, for example, one substrate wassubjected to photo-alignment treatment and PS treatment and the othersubstrate was subjected to rubbing treatment, in a liquid crystaldisplay device; and the influence of hysteresis and the like on themonomer concentration for PS treatment in liquid crystal wereinvestigated (for example, see Non-Patent Literature 1).

CITATION LIST Patent Literatures

-   Patent Literature 1: Japanese Patent No. 4175826-   Patent Literature 2: Japanese Patent No. 4237977-   Patent Literature 3: JP-A 2005-181582-   Patent Literature 4: JP-A 2004-286984-   Patent Literature 5: JP-A 2009-102639-   Patent Literature 6: JP-A 2009-132718-   Patent Literature 7: JP-A 2010-33093-   Patent Literature 8: U.S. Pat. No. 6,177,972-   Patent Literature 9: JP-A 2003-177418

Non-Patent Literature

-   Non-Patent Literature 1: Y. Nagatake et al. “Hysteresis Reduction in    EO Characteristic of Photo-Aligned IPS-LCDs with    Polymer-Surface-Stabilized Method”, IDW '10, International Display    Workshops, 2010, pp. 89-92

SUMMARY OF INVENTION Technical Problem

The present inventors have been studying photo-alignment technique thatallows the liquid crystal alignment direction to be controlled inmultiple directions when a voltage is applied, without the need ofrubbing treatment on an alignment film, and that provides excellentviewing angle characteristic. The photo-alignment technique is atechnique of irradiating an alignment film, which is formed from alight-active material, with light such as ultraviolet light, and therebycausing the alignment film to have an alignment regulating force.

According to the photo-alignment technique, since alignment treatmentcan be performed on a film surface in a non-contact manner, theoccurrence of contaminants, dust and the like during alignment treatmentcan be suppressed. Additionally, unlike rubbing treatment, thephoto-alignment technique can be suitably applied even to large panels,and can achieve excellent manufacturing yield.

The current photo-alignment technique has been adopted mainly for themass production of televisions in which a vertical alignment film isused (for example, VA mode). The current photo-alignment technique hasnot been adopted for the mass production of televisions in which ahorizontal alignment film is used (for example, IPS mode). This isbecause the use of a horizontal alignment film causes image sticking ina conspicuous manner. The image sticking is a phenomenon in which whenthe same amount of voltage is continuously applied for a certain periodof time to a liquid crystal cell, brightness appears different between aportion where the voltage is continuously applied and a portion wherethe voltage is not applied.

The present inventors have found that forming a polymer layer stabilizedby PS treatment is suitable to reduce the occurrence of image stickingcaused by weak anchoring of the photo-alignment film. Therefore, it isimportant to promote polymerization to allow PS treatment. In addition,as described in Japanese Patent Application No. 2011-084755, acombination of a specific liquid crystal component with PS treatmentprocess is suitable. This increases a polymer layer formation rate(i.e., the rate at which a polymer layer is formed, as a polymerizablemonomer in the liquid crystal layer initiates chain polymerization suchas radical polymerization, and the polymerized product is deposited onthe surface on the liquid crystal layer side of the alignment film), andallows the formation of a polymer layer having a stable alignmentregulating force (i.e., a PS layer). Further, the effect of reducingimage sticking is particularly excellent when the alignment film is ahorizontal alignment film because it increases the polymerization rateand the polymer layer formation rate.

Herein, for example, when PS treatment is performed in order to preventimage sticking in a horizontal electric field alignment mode such as anIPS mode or an FFS mode in which a horizontal photo-alignment film isused, alignment defects in the panel, if occurred, will be immobilized,leading to display defects. Among alignment defects, the occurrence of astring-like defect is particularly problematic. The string-like defectrefers to a phenomenon that causes light leakage due to a string-likealignment defect in liquid crystal. The impacts of the light leakage onthe quality of the liquid crystal display device are as follows: blackappears grayish black; the contrast is poor; and the display becomesrough. None of the above-mentioned Patent Literatures 1 to 8 describesthe horizontal photo-alignment film and the occurrence of a string-likedefect caused by weak anchoring.

The importance of an object to reduce string-like defects isparticularly significant when aiming to mass-produce liquid crystaldisplay devices including a horizontal photo-alignment film having aweak alignment regulating force. It is considered to be a novel objectin the technical field of the present invention.

For example, Patent Literature 9 mentioned above provides a liquidcrystal display device having improved light transmittance, withoutdecreasing the response speed when a change occurs in the gray scale.According to Embodiment 6-2 of Patent Literature 9, alignment defectsoccur due to the unevenness of the uneven reflective electrodes, andrubbing treatment fails to provide sufficient alignment treatment on thebottom of the uneven surface. In this respect, the occurrence ofdisclinations due to alignment disturbance can be suppressed by forminga polymer layer on the uneven reflective electrodes. However, this doesnot solve the problem of disclinations resulting from immobilization ofalignment defects during PS treatment in the liquid crystal displaydevice including a horizontal photo-alignment film having a weakalignment regulating force. Unfortunately, disclinations that occurbefore PS treatment are strongly immobilized as the disclinations by PStreatment. The technique disclosed in Non-Patent Literature 1 has a roomfor further improvement to suitably reduce disclinations that occur indisplay pixels due to PS treatment in the liquid crystal display deviceincluding a horizontal photo-alignment film.

The present invention is achieved in view of the current situationdescribed above. It is an object of the present invention to provide aliquid crystal display panel and a liquid crystal display device havingexcellent display quality, with reduced string-like defects that occurin display pixels.

Solution to Problem

The present inventors conducted extensive studies and found that theabove type of string-like defects occurs due to the following threefactors. The first factor is weak anchoring of the alignment filmitself. The present inventors found that weak anchoring of the alignmentfilm results in a weak alignment regulating force, causing liquidcrystal molecules in the bulk to easily stray from the direction inwhich the alignment film is treated. In other words, a method ofincreasing the anchoring strength of the alignment film itself isconsidered as a possible solution to the problem; however, usually, theanchoring energy of a horizontal photo-alignment film is remarkablysmall, compared to a horizontal alignment film to be rubbed. Thus, theapproach to the problem by improving the properties of a material of thehorizontal photo-alignment film has been difficult to apply. The secondfactor is a small elastic constant of liquid crystal. The presentinventors found that when the elastic constant is small, liquid crystalmolecules tend to undergo elastic deformation, and alignment disturbanceis thus likely to occur. The string-like defect is considered to be analignment defect resulting from splay deformation and/or benddeformation; thus, liquid crystal having a large elastic constant forsplay deformation and bend deformation is considered to be less likelyto produce alignment defects. The third factor is the presence ofspacers. The present inventors found that a spacer is present at bothends of each string-like defect. For example, even when string-likedefects occurred at the moment of phase transition from the isotropicphase to the liquid crystal phase, the string-like defects in the areawhere no spacer is present were observed to be unstable and disappear ina finite time. In other words, the spacers are considered to have aneffect of stabilizing string-like defects, and the present inventorsexamined a method for decreasing the occurrence of such string-likedefects in display pixels.

Then, the present inventors found a suggestion for improvement: it is toalign liquid crystal molecules in a specific direction in accordancewith the arrangement of spacers such as photospacers. In other words, itis to provide a liquid crystal display panel including multiple spacersbetween a pair of substrates, wherein in a plan view of the main surfaceof the pair of substrates, the spacers are arranged such that aninter-spacer distance between adjacent spacers in a longitudinaldirection is different from an inter-spacer distance between adjacentspacers in a transverse direction, and an angle formed between a lineconnecting the spacers with a shorter inter-spacer distance than theother inter-spacer distance and an alignment direction of the liquidcrystal molecules at a voltage lower than a threshold voltage in theliquid crystal layer is 20° or smaller. This configuration sufficientlyreduces string-like defects in display pixels, as described later. Thepresent inventors found that the above problem can be successfullysolved in this manner, and thus accomplished the present invention. Asanother suggestion for improvement, the applicant of the presentinvention has suggested increasing an elastic constant K1 (splay) and/oran elastic constant K3 (bend) of liquid crystal in an earlierapplication (Japanese Patent Application No. 2011-051532).

That is, one aspect of the present invention relates to a liquid crystaldisplay panel including: a pair of substrates, and a liquid crystallayer interposed between the pair of substrates, wherein at least one ofthe pair of substrates includes a photo-alignment film and an electrodein the stated order from the liquid crystal layer side; thephoto-alignment film aligns liquid crystal molecules horizontally to amain surface of the at least one of the pair of substrates; the liquidcrystal display panel includes multiple spacers between the pair ofsubstrates, the spacers being arranged such that an inter-spacerdistance between adjacent spacers in a longitudinal direction isdifferent from an inter-spacer distance between adjacent spacers in atransverse direction in a plan view of the main surface of the pair ofsubstrates; and an angle formed between a line connecting the spacerswith a shorter inter-spacer distance than the other inter-spacerdistance and an alignment direction of the liquid crystal molecules at avoltage lower than a threshold voltage in the liquid crystal layer is20° or smaller.

The photo-alignment film aligns the liquid crystal moleculeshorizontally to the main surface of the at least one of the pair ofsubstrates (the photo-alignment film as used herein is also referred toas “horizontal photo-alignment film”). The horizontal photo-alignmentfilm is not limited as long as it aligns at least liquid crystalmolecules adjacent thereto, substantially horizontally to the surface ofthe horizontal photo-alignment film. It is possible to form a morestable PS layer in this manner because the transfer of the excitationenergy from the alignment film to the monomer when a photoactivematerial is irradiated with light is more efficiently performed in ahorizontal alignment film than in a vertical alignment film.

The at least one of the pair of substrates preferably further includes apolymer layer on the liquid crystal layer side of the horizontalphoto-alignment film.

Hereinafter, features of the liquid crystal display panel of the presentinvention and preferred features thereof are described in detail.

Herein, although the longitudinal direction is not particularly limited,it usually refers to a direction along a source bus line, and itincludes a substantially longitudinal direction as long as the effectsof the present invention are achieved. The transverse direction usuallyrefers to a direction along a gate bus line. It includes a substantiallytransverse direction as long as the effects of the present invention areachieved.

The liquid crystal display panel of the present invention includesmultiple spacers between the pair of substrates, the spacers beingarranged such that the inter-spacer distance between adjacent spacers inthe longitudinal direction is different from the inter-spacer distancebetween adjacent spacers in the transverse direction in a plan view ofthe main surface of the pair of substrates. For example, the liquidcrystal display panel may be configured as follows: in a plan view ofthe main surface of the pair of substrates, when a total of threespacers are selected including a spacer as a reference, a spacer that isadjacent to the reference spacer in the longitudinal direction, and aspacer that is adjacent to the reference spacer in the transversedirection, the inter-spacer distance between adjacent spacers in thelongitudinal direction is different from that in the transversedirection; and an angle formed between a line connecting the spacerswith a shorter inter-spacer distance and the alignment direction of theliquid crystal molecules at a voltage lower than a threshold voltage inthe liquid crystal layer is 20° or smaller.

A preferred embodiment of the liquid crystal display panel of thepresent invention is as follows: in a plan view of the main surface ofthe pair of substrates, the spacers are regularly aligned at regularintervals in the longitudinal and transverse directions such that theinter-spacer distance between adjacent spacers in the longitudinaldirection of the unit cell is different from that in the transversedirection of the unit cell. The phrase “the spacers are regularlyaligned at regular intervals in the longitudinal and transversedirections such that the inter-spacer distance between adjacent spacersin the longitudinal direction of the unit cell is different from that inthe transverse direction” means that, for example, the spacers areregularly aligned at regular intervals d_(l) in the longitudinaldirection and at regular intervals d_(w) in the transverse direction,and the values of d_(l) and d_(w) are different from each other. Inother words, the spacers are located at the intersections of the grid inwhich the vertical length of the unit cell is different from thehorizontal length thereof. The phrase “regularly aligned” may refer toan alignment in which some of the spacers are not regularly aligned: itsuffices if the spacers are substantially regularly aligned. In otherwords, the spacers do not have to be located at every intersection ofthe grid. It suffices if the spacers are located substantially at theintersections of the grid, as long as the effects of the presentinvention are achieved.

The spacers in the liquid crystal display panel of the present inventionare preferably regularly aligned at regular intervals in thelongitudinal and transverse directions, i.e., the spacers are preferablyregularly located at the intersections of the grid in which the verticallength of the unit cell is different from the horizontal length thereof.However, the spacers in the liquid crystal display panel do not have tobe regularly aligned at regular intervals in either longitudinal ortransverse direction. In this case, the direction of a line connectingthe spacers with a shorter inter-spacer distance may differ, dependingon how spacers adjacent to a reference spacer in the longitudinal andtransverse directions are selected after such a reference spacer isselected. In this case, a line connecting the spacers with the shortestinter-spacer distance among the inter-spacer distances between adjacentspacers in the longitudinal and transverse directions maybe regarded as“a line connecting the spacers with a shorter inter-spacer distance”.

In the liquid crystal display panel of the present invention, when theinter-spacer distance between neighboring spacers in the longitudinaldirection is compared with the inter-spacer distance between neighboringspacers in the transverse direction, a shorter inter-spacer distance is,for example, preferably ⅘ or less of a longer inter-spacer distance. Ashorter inter-spacer distance is also preferably ⅕ or more of a longerinter-spacer distance. In a plan view of the main surface of the pair ofsubstrates, each spacer is preferably regularly located at eachintersection of the grid, for example, near the top of each pixel. Inaddition, the spacers are preferably arranged so as to be superimposedwith the black matrix, in a plan view of the main surface of the pair ofsubstrates. For example, preferably, the black matrix is arranged in agrid pattern, and the spacers are arranged so as to be superimposed withthe intersections of the grid-like black matrix. The sectionspartitioned by the grid-like black matrix may be, for example, pixels.

The liquid crystal display panel of the present invention is configuredsuch that an angle formed between a line connecting the spacers with ashorter inter-spacer distance than the other inter-spacer distance andthe alignment direction of the liquid crystal molecules at a voltagelower than a threshold voltage in the liquid crystal layer is 20° orsmaller.

The “alignment direction of the liquid crystal molecules” refers to adirection of the long axis of the liquid crystal molecules. In otherwords, it refers to the director. The phrase that “an angle formedbetween a line connecting the spacers and the alignment direction of theliquid crystal molecules is 20° or smaller” may mean that an angleformed between a line connecting the spacers with a shorter inter-spacerdistance and the alignment direction of the liquid crystal moleculesnear the line is 20° or smaller in a plan view of the main surface ofthe pair of substrates. It may also mean that an angle formed between aline connecting the spacers with a shorter inter-spacer distance and theaverage alignment direction of the liquid crystal molecules in theentire liquid crystal layer is 20° or smaller in a plan view of the mainsurface of the pair of substrates. The liquid crystal is aligned in auniform direction in the most area at a voltage lower than a thresholdvoltage.

The “threshold” refers to a voltage that generates an electric field inwhich the liquid crystal layer undergoes optical changes, and thedisplay state thus changes in the liquid crystal display device. The“threshold voltage” refers to, for example, a voltage at which thetransmittance is 5% when the transmittance in the bright state is set to100%. An electric potential difference can be created at a level higherthan or equal to the threshold voltage. It means that the liquid crystaldisplay device can be operated in such a manner that creates an electricpotential difference at a level higher than or equal to the thresholdvoltage. Thereby, an electric field that is applied to the liquidcrystal layer can be suitably controlled.

If the number of spacers in the entire area of the liquid crystaldisplay panel is assumed to be 100%, 50% or more of the spacers arepreferably configured such that the liquid crystal molecules are alignedsubstantially parallel to a line connecting the adjacent spacers with ashort inter-spacer distance. More preferably, substantially all of thespacers in the entire area of the liquid crystal display panel areconfigured as described above.

In addition, the spacers with a shorter inter-spacer distance preferablyrefer to the nearest adjacent spacers in the liquid crystal displaypanel in a plan view of the main surface of the pair of substrates. The“nearest adjacent spacers” refers to the spacers with the shortestinter-spacer distance among the inter-spacer distances between adjacentspacers in the longitudinal and transverse directions in the liquidcrystal display panel in which the spacers are regularly arranged. Theliquid crystal display panel of the present invention may be configuredas described above such that an angle formed between a line connectingthe nearest adjacent spacers with the shortest inter-spacer distanceamong the inter-spacer distances and the alignment direction of theliquid crystal molecules at a voltage lower than a threshold voltage inthe liquid crystal layer is 20° or smaller. Such a configuration isanother preferred embodiment of the present invention.

The line connecting the spacers with a shorter inter-spacer distance ispreferably parallel to the alignment direction of the liquid crystalmolecules at a voltage lower than a threshold voltage in the liquidcrystal layer. The “parallel” direction includes a direction that isconsidered to be parallel in the technical field of the presentinvention, and it also includes a substantially parallel direction. Theeffects of the present invention can be remarkably excellent in themanner described above.

The spacers maybe disposed by being dispersed or the like. Preferably,the spacers are photospacers disposed on the at least one of the pair ofsubstrates and projecting toward the liquid crystal layer. The spacersdisposed on the substrate (s) in advance are usually formed of resin.The spacers disposed by being dispersed or the like are usually formedof glass or plastic. The above spacers are preferably those formed ofresin, disposed on the substrate(s). More preferably, the resin isacrylic resin. Examples of the shape of each spacer include cylinder,prism, truncated cone, and sphere. Cylinder, prism, and truncated coneare preferred. The spacer may be coated with the horizontalphoto-alignment film. The spacer is regarded as being coated with thehorizontal photo-alignment film, as long as at least a portion of thespacer in contact with the liquid crystal layer (usually, a lateralside) is coated with the horizontal photo-alignment film. The substrateon which the spacers are disposed is preferably a counter substrate(color filter substrate).

Each of the photospacers preferably has a diameter of 14 μm or less asmeasured on the base (the surface in contact with the at least one ofthe pair of substrates) in order to more sufficiently achieve theeffects of the present invention. The diameter is more preferably 12 μmor less. The diameter of the base is described later.

The liquid crystal molecules in the liquid crystal layer of the presentinvention may include a mixture of plural kinds of liquid crystalmolecules. The liquid crystal layer may be a mixture of plural kinds ofliquid crystal molecules for at least one of the following purposes:ensuring reliability; improving the response speed; and adjusting theliquid crystal phase temperature range, other elastic constants,anisotropy of dielectric constant, and refractive index anisotropy. Inthe case where the liquid crystal molecules in the liquid crystal layerinclude a mixture of plural kinds of liquid crystal molecules, theliquid crystal molecules as a whole must be designed to have an elasticcoefficient of the present invention. In addition, the liquid crystalmolecules in the liquid crystal layer may have either positiveanisotropy of dielectric constant (positive type) or negative anisotropyof dielectric constant (negative type).

At least one of the pair of substrates included in the liquid crystaldisplay panel of the present invention includes, for example, a polymerlayer, a horizontal photo-alignment film, and an electrode in the statedorder from the liquid crystal layer side. A different layer may bepresent between the polymer layer and the horizontal photo-alignmentfilm and/or between the horizontal photo-alignment film and theelectrode. As long as the effects of the present invention are achieved,another layer may be provided between the polymer layer and thehorizontal photo-alignment film, and/or between the horizontalphoto-alignment film and the electrode. Usually, the polymer layer andthe horizontal photo-alignment film are in contact with each other. Inaddition, preferably, each of the pair of substrates includes thehorizontal photo-alignment film and the polymer layer. Preferably, theat least one of the pair of substrates further includes a linearelectrode.

The horizontal photo-alignment film of the present invention ispreferably, but not limited to, an alignment film having a property ofaligning liquid crystal molecules adjacent thereto in a certaindirection. The horizontal photo-alignment film also encompasses a filmon which alignment treatment or the like is not performed and thus hasno alignment property. In other words, the present invention isapplicable to: polymer stabilization treatment to extend the BPtemperature range in a polymer-stabilized blue phase (BP) display devicein which alignment treatment is not required in the first place; aprocess for partially polymerizing a liquid crystal layer in a polymerdispersed liquid crystal (PDLC) display device; and other variousapplications. Specifically, the present invention is not only applicableto PS treatment to prevent image sticking, but is also applicable toother applications that require the formation of a polymer from apolymerizable monomer in a liquid crystal layer, as long as the presentinvention is a liquid crystal display panel including a polymer layer.Photo-alignment treatment is preferred as a method of performingalignment treatment because the effects of the present invention will bemore significant, and excellent viewing angle characteristic can beobtained. Alignment treatment may also be performed by rubbing or thelike.

The horizontal photo-alignment film achieves photo-alignment treatmentthat imparts an alignment property to the substrate surfaces throughlight irradiation with certain conditions. Hereinafter, a polymer filmhaving a property of controlling the alignment of liquid crystal throughphoto-alignment treatment is also referred to as “photo-alignment film”.

A polymer constituting the horizontal photo-alignment film is preferablypolysiloxane, polyamide acid, or polyimide, in terms of heat resistance.

The horizontal photo-alignment film is a polymer film having anisotropyinduced by polarized or non-polarized light irradiation and having aproperty of imparting an alignment regulating force to liquid crystal.More preferably, the horizontal photo-alignment film is aphoto-alignment film on which photo-alignment treatment is performed byultraviolet light, visible light, or both of them. The size of thepretilt angle that is imparted to the liquid crystal molecules by thephoto-alignment film can be adjusted by the type of light, lightirradiation time, irradiation direction, irradiation intensity, type ofphotofunctional groups, and the like. It should be noted that becausethe alignment is immobilized by the formation of the polymer layer,there is no need to prevent ultraviolet light or visible light fromentering the liquid crystal layer after the production process, and thusthe range of selection of the production processes is broadened. Inaddition, when the horizontal photo-alignment film having a property ofaligning liquid crystal molecules vertically to irradiated polarizedlight is irradiated with p-polarized light in a normal direction of thesubstrate or in an oblique direction to the substrate, the pretilt angleis 0°.

The photoactive material is preferably a material of the photo-alignmentfilm. The material of the photo-alignment film may be a single polymeror a mixture containing other molecules as long as the material has theproperty described above. For example, the material may also be amixture obtained by adding other low molecular weight molecules such asadditives or other photo-inactive polymers to a polymer containing afunctional group having photo-alignment ability. As the material of thephoto-alignment film, a material which induces photodissociation,photoisomerization, or photodimerization is selected. Generally,photoisomerization and photodimerization allow alignment at a longerwavelength with a smaller exposure dose and thus exhibit excellent massproductivity, compared to photodissociation. In other words, thephoto-alignment film used in the present invention preferably includes aphotoreactive functional group capable of undergoing photoisomerizationor photodimerization.

Representative materials that induce photoisomerization orphotodimerization include azobenzene derivatives, cinnamoyl derivatives,chalcone derivatives, cinnamate derivatives, coumarin derivatives,diarylethene derivatives, stilbene derivatives, and anthracenederivatives. The material for photoisomerization or photodimerization ispreferably a cinnamate group or a derivative thereof. In other words,the photo-alignment film preferably includes a functional group having acinnamate derivative. The benzene ring that is present in thesefunctional groups may be a heterocyclic ring. A representative materialthat induces photodissociation is a material including a cyclobutaneskeleton. Examples thereof include polyimide including a cyclobutanering. In one preferred embodiment of the present invention, a materialof the photo-alignment film (a material constituting the photo-alignmentfilm) includes a cyclobutane skeleton in a repeating unit.

The horizontal photo-alignment film may be a horizontal photo-alignmentfilm irradiated with ultraviolet light from the outside of the liquidcrystal cell. In this case, when the horizontal photo-alignment film isformed through photo-alignment treatment, and the polymer layer isformed through photopolymerization, it is preferred that the horizontalphoto-alignment film and the polymer layer be simultaneously formed byusing the same light. This provides a liquid crystal display panel withhigh production efficiency.

The polymer layer of the present invention is preferably a polymerizedproduct of a monomer contained in the liquid crystal layer. In otherwords, the polymer layer is preferably the PS layer described above.Usually, the PS layer controls the alignment of liquid crystal moleculesadjacent thereto. A polymerizable functional group of the monomer ispreferably at least one selected from the group consisting of acrylate,methacrylate, vinyl, vinyloxy, and epoxy groups. Among these, anacrylate group and/or a methacrylate group is more preferred.

These polymerizable functional groups are highly likely to produceradicals, and are effective in reducing manufacturing cycle time. Inaddition, the monomer preferably includes at least two polymerizablefunctional groups because the reaction efficiency is higher when thenumber of polymerizable functional groups is larger. Further, an upperlimit of the number of polymerizable functional groups in the monomer ispreferably four, so that the molecular weight is sufficiently reducedand the monomer can thus be easily dissolved in liquid crystal. Inaddition, the monomer is preferably a monomer that initiatespolymerization by light irradiation (i.e., photopolymerization) or amonomer that initiates polymerization by heating (i.e., thermalpolymerization). In other words, the polymer layer is preferably formedby photopolymerization or thermal polymerization.

Photopolymerization is particularly preferred because the polymerizationreaction can be easily initiated at normal temperature. The light usedfor photopolymerization is preferably ultraviolet light, visible light,or a combination thereof.

In the present invention, the type of polymerization reaction to formthe PS layer is not particularly limited, and examples thereof includestep-growth polymerization in which a bifunctional monomer ispolymerized stepwise while forming a new bond; and chain polymerizationin which a monomer is sequentially bonded to active species generatedfrom a small amount of catalyst (initiator) and are grown in a chainreaction. Examples of the step-growth polymerization includepolycondensation and polyaddition. Examples of the chain polymerizationinclude radical polymerization and ionic polymerization (for example,anionic polymerization and cationic polymerization).

The polymer layer improves the alignment regulating force of thehorizontal photo-alignment film on which alignment treatment has beenperformed, and can reduce the occurrence of image sticking in display.In addition, in the case where a voltage of a threshold or higher isapplied to the liquid crystal layer to polymerize a monomer in a statewhere liquid crystal molecules are aligned at a pre-tilt angle so as toform a polymer layer, the thus-obtained polymer layer includes astructure that allows the liquid crystal molecules to be aligned at apre-tilt angle with respect to the polymer layer.

The pair of substrates included in the liquid crystal display panel ofthe present invention is used for interposing a liquid crystal layertherebetween. Each substrate is produced by, for example, forming awiring, an electrode, a color filter, and the like on an insulatingsubstrate as a base formed of glass, resin, or the like. The electrodecan be suitably selected in accordance with the alignment mode and thelike. Preferred examples thereof include a linear electrode.

The alignment mode of the liquid crystal layer is preferably analignment mode in which a horizontal alignment film can be used.Preferred examples thereof include in-plane switching (IPS), fringefield switching (FFS), optically compensated birefringence (OCB),twisted nematic (TN), super twisted nematic (STN), ferroelectrics liquidcrystal (FLC), anti-ferroelectrics liquid crystal (AFLC), polymerdispersed liquid crystal (PDLC), and polymer network liquid crystal(PNLC) modes. Among these, the IPS, FFS, FLC, and AFLC modes are morepreferred, and the IPS and FFS modes are still more preferred. Inaddition, a blue phase mode in which the formation of an alignment filmis unnecessary is also preferred as the above alignment mode. Further, amode in which the at least one of the pair of substrates includes amulti-domain structure for improving viewing angle characteristic isalso preferred as the above alignment mode. The multi-domain structurerefers to a structure including plural areas in which the liquid crystalmolecules have different alignment forms (for example, in terms of benddirections in the OCB mode or twist directions in the TN and STN modes)or different alignment directions during either or both voltageapplication and non-voltage application. Forming the multi-domainstructure actively requires patterning of an electrode into anappropriate form, and/or irradiation of a photoactive material withlight using a photomask or the like.

As described above, the present invention is suitably applicable fordisplay devices having excellent viewing angles such as an IPS mode oran FFS mode. A technique that provides good viewing angles is requiredin applications such as medical monitors, electronic books, smartphones,and the like.

The present invention also provides a liquid crystal display deviceincluding the liquid crystal display panel of the present invention.Preferred embodiments of the liquid crystal display panel included inthe liquid crystal display device of the present invention are the sameas those of the liquid crystal display panel of the present inventiondescribed above. In one preferred embodiment of the present invention,the liquid crystal display device of the present invention is a liquidcrystal display device of an IPS mode. In another preferred embodimentof the present invention, the liquid crystal display device of thepresent invention is a liquid crystal display device of an FFS mode. Theliquid crystal display device of an IPS mode is a liquid crystal displaydevice of a horizontal electric field mode in which, usually, one of thepair of substrates includes two types of electrodes, which are opposedto each other when the main surface of the substrate is viewed in plane.In addition, the liquid crystal display device of an FFS mode is aliquid crystal display device of a fringe electric field mode in which,usually, one of the pair of substrates includes a planar electrode, anda slit electrode disposed in a layer different from a layer includingthe planar electrode, with an insulation layer between these layers.These liquid crystal display devices are described in further detail inembodiments.

As long as the above-described constituent elements are included asessential elements, the liquid crystal display panel and the liquidcrystal display device of the present invention are not particularlylimited by other constituent elements, and may appropriately includeother elements that are commonly included in liquid crystal displaypanels and liquid crystal display devices.

Each of the embodiments described above may be appropriately combinedwithout departing from the scope of the present invention.

Advantageous Effects of Invention

The present invention provides a liquid crystal display panel and aliquid crystal display device having excellent display quality, withreduced string-like defects that occur in display pixels. When thepresent invention is applied to, for example, a liquid crystal displaydevice of an IPS mode or an FFS mode including a photo-alignment film,an excellent viewing angle is achieved owing to the properties of aphoto-alignment film, and the effect of reducing image sticking is alsoachieved at the same time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a planar schematic diagram showing spacer arrangement andalignment of liquid crystal molecules in a liquid crystal display panelaccording to Embodiment 1.

FIG. 2 is a planar schematic diagram showing spacer arrangement in aliquid crystal display panel according to Embodiment 1.

FIG. 3 is a view showing alignment and alignment singularities of liquidcrystal molecules in a liquid crystal display panel according toEmbodiment 1.

FIG. 4 is a planar schematic diagram showing a counter substrateaccording to Embodiment 1.

FIG. 5 is a cross-sectional schematic diagram showing a liquid crystaldisplay panel according to Embodiment 1.

FIG. 6 is a planar schematic diagram showing a slit electrode accordingto Embodiment 1.

FIG. 7 is a cross-sectional schematic diagram showing an embodiment of aliquid crystal display panel according to a modified example ofEmbodiment 1.

FIG. 8 is a planar schematic diagram showing a pair of combteethelectrodes according to a modified example of Embodiment 1.

FIG. 9 is a planar schematic diagram showing spacer arrangement andalignment of liquid crystal molecules in a liquid crystal display panelaccording to Comparative Embodiment 1.

FIG. 10 is a view showing alignment and alignment singularities ofliquid crystal molecules in a liquid crystal display panel according toComparative Embodiment 1.

FIG. 11 is an image showing a display area of a liquid crystal displaypanel according to Comparative Example 1.

FIG. 12 is a planar schematic diagram showing a grid-like black matrixand photospacers in the present embodiment.

FIG. 13 is a cross-sectional schematic diagram of FIG. 12.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention is described in further detail byexplaining embodiments with reference to the drawing, but is not limitedto these embodiments. The term “pixel” as used herein may refer to asubpixel, unless otherwise specified. In addition, the substrateincluding a thin film transistor element is also referred to as a TFTsubstrate, and a color filter substrate is also referred to as a CFsubstrate. In the embodiments, string-like defects were measured byobserving every pixel of a panel prepared, under a polarizingmicroscope. Members and parts having the same functions are denoted bythe same reference numerals except for the hundred's digit throughoutthe embodiments, unless otherwise specified. The terms “or more” and “orless” as used herein are inclusive. In other words, the term “or more”means “greater than and equal to” the value specified.

Embodiment 1

FIG. 1 is a planar schematic diagram showing spacer arrangement andalignment of liquid crystal molecules in a liquid crystal display panelaccording to Embodiment 1. In the present embodiment, the photospacersare arranged at regular intervals of 150 μm in the longitudinaldirection and 50 μm in the transverse direction. The photospacers areregularly located at the intersections of the grid in which the verticallength of the unit cell is 150 μm and the horizontal length of the unitcell is 50 μm. The spacers are preferably arranged so as to besuperimposed with the black matrix. In addition, it is more preferredthat the black matrix be arranged in a grid pattern, and the spacers bearranged so as to be superimposed with the intersections of thegrid-like black matrix. Herein, the sections partitioned by thegrid-like black matrix may be pixels.

As described later, for liquid crystal alignment treatment, thesesubstrates were irradiated with linearly polarized ultraviolet lighthaving a wavelength of 313 nm and an intensity of 5 J/cm² from thenormal direction of the substrates. An angle formed between a lineconnecting two nearest adjacent photospacers (a photospacer 29 a and aphotospacer 29 b) and a polarization direction (not shown) is 90°. Inother words, the angle formed between a line connecting the photospacer29 a and the photospacer 29 b and a liquid crystal alignment direction32 at a voltage lower than a threshold voltage is 0°, and the lineconnecting the two nearest adjacent photospacers is parallel to theliquid crystal alignment direction. The advantageous effects of thepresent invention can be achieved by the liquid crystal display panel,wherein in a plan view of the main surface of the pair of substrates,the spacers are arranged such that the inter-spacer distance between theadjacent spacers in the longitudinal direction is different from that inthe transverse direction, and the angle formed between the lineconnecting the spacers with a shorter inter-spacer distance than theother inter-spacer distance and the alignment direction of the liquidcrystal molecules at a voltage lower than a threshold voltage in theliquid crystal layer is substantially 0°.

FIG. 2 is a planar schematic diagram showing spacer arrangement in aliquid crystal display panel according to Embodiment 1. The presentinvention may be configured as follows: when a total of three spacersthat are adjacent in the longitudinal and transverse directions areselected in a plan view of the main surface of the pair of substrates,the inter-spacer distance between the adjacent spacers in thelongitudinal direction is different from that in the transversedirection; and the angle formed between the line connecting the spacerswith a shorter inter-spacer distance and the alignment direction of theliquid crystal molecules at a voltage lower than a threshold voltage inthe liquid crystal layer is 20° or smaller. For example, when threespacers (the photospacer 29 a, a photospacer 29 c, and a photospacer 29d) are selected, an inter-spacer distance l_(ca) between the adjacentphotospacers 29 a and 29 c in the longitudinal direction may bedifferent from an inter-spacer distance l_(cd) between the adjacentphotospacers 29 c and 29 d in the transverse direction, and an angleformed between a line connecting the photospacers 29 c and 29 d with theshorter inter-spacer distance l_(cd) and the alignment direction of theliquid crystal molecules at a voltage lower than a threshold voltage inthe liquid crystal layer may be 20° or smaller. In addition, when threespacers (the photospacer 29 c, the photospacer 29 d, and a photospacer29 e) are selected, an inter-spacer distance l_(ce) between the adjacentphotospacers 29 c and 29 e in the longitudinal direction may bedifferent from an inter-spacer distance l_(cd) between the neighboringphotospacers 29 c and 29 d in the transverse direction, and an angleformed between a line connecting the photospacers 29 c and 29 d with theshorter inter-spacer distance l_(cd) and the alignment direction of theliquid crystal molecules at a voltage lower than a threshold voltage inthe liquid crystal layer may be 20° or smaller.

In the case where the spacers are not regularly arranged at regularintervals in either longitudinal or transverse direction (for example,the length is different between l_(ca) and l_(ce): l_(ca) is longer thanl_(cd), and l_(ce) is shorter than l_(cd)), the direction of a lineconnecting the spacers with a shorter inter-spacer distance may differ,depending on how spacers adjacent to a reference spacer in thelongitudinal and transverse directions are selected after such areference spacer is selected. In this case, a line connecting thespacers with the shortest inter-spacer distance among the inter-spacerdistances between adjacent spacers in the longitudinal and transversedirections maybe regarded as “a line connecting the spacers with ashorter inter-spacer distance”.

FIG. 3 is a view showing alignment and alignment singularities of liquidcrystal molecules in a liquid crystal display panel according toEmbodiment 1. A string-like defect 34 easily occurs between the nearestadjacent photospacers (between the photospacer 29 a and the photospacer29 b). This is because the length of the string-like defect 34 increasesin proportion to the energy of the defect, and the shorter thestring-like defect 34, the more energetically stable it becomes. InEmbodiment 1, the photospacers are located at the intersections of agrid in which the vertical length of the unit cell is 150 μm and thehorizontal length of the unit cell is 50 μm. Thus, the string-likedefect 34 easily occurs between the photospacers arranged at shorterintervals of 50 μm.

Generally, PI (polyimide) is hardly attached around the photospacers.Thus, the liquid crystal molecules are aligned along the photospacers(see a liquid crystal alignment direction 32 p in FIG. 3). In the casewhere a photo-alignment treatment has been performed, alignmentsingularities 36 are present at the three o'clock position (right side)and the nine o'clock position (left side) of the photospacers 29 a and29 b, as shown in FIG. 3 in Embodiment 1. In Embodiment 1, thestring-like defect 34 does not project to the outside of the blackmatrix (BM), and the string-like defects that occur in display pixelscan be sufficiently reduced, compared to the later-described ComparativeExample 1.

FIG. 4 is a planar schematic diagram showing a counter substrate (CFsubstrate) according to Embodiment 1. Spacers 29 are arranged atintervals of 150 μm in the longitudinal direction and 50 μm in thetransverse direction on the black matrix (BM). These spacers cannot beobserved with transmitted light (in FIG. 4, the spacers were observedwith reflected light).

FIG. 5 is a cross-sectional schematic diagram showing a liquid crystaldisplay panel according to Embodiment 1. As shown in FIG. 5, the liquidcrystal display panel of Embodiment 1 includes a pair of substratesconsisting of a TFT substrate 10 and a CF substrate 20, and a liquidcrystal layer 30 interposed between the pair of substrates. The TFTsubstrate 10 includes: an insulating transparent substrate 15 formed ofglass or the like; a slit electrode 12 on an upper layer; a lower layerelectrode 14 on a lower layer; and an insulation layer 13 between theslit electrodes 12 and the lower layer electrode (planar electrode) 14.Usually, the slit electrode 12 on the upper layer is a signal electrode,and the lower layer electrode 14 is a common electrode. The electrode onthe upper layer may be, for example, a pair of combteeth electrodes,instead of the slit electrode. The CF substrate 20 includes aninsulating transparent substrate 25 formed of glass or the like; a colorfilter (not shown) formed on the transparent substrate 25; and a blackmatrix (not shown) formed on the same. Other elements such as a commonelectrode may further be included, if necessary. For example, althoughthe FFS mode as in Embodiment 1 includes the electrodes (the slitelectrode 12 and the lower layer electrode 14) only on the TFT substrate10 as shown in FIG. 5, the present invention is applicable to othermodes, and in that case, the electrodes are formed on both of the TFTsubstrate 10 and the counter substrate 20, if necessary.

The TFT substrate 10 also includes an alignment film (horizontalphoto-alignment film) 16, and the CF substrate 20 also includes analignment film (horizontal photo-alignment film) 26. The alignment films16 and 26 are films mainly including polyimide, polyamide, polyvinyl,polysiloxane, and the like. Forming these alignment films allows liquidcrystal molecules to be aligned in a certain direction.

Prior to a PS polymerization process, the liquid crystal layer 30contains a polymerizable monomer. The polymerizable monomer initiatespolymerization by the PS polymerization process to form PS layers 17 and27 on the alignment films 16 and 26, respectively, as shown in FIG. 5,thus improving the alignment regulating force of the alignment films 16and 26.

The PS layers 17 and 27 can be formed by injecting a liquid crystalcomposition containing a liquid crystal material and a polymerizablemonomer into a gap between the TFT substrate 10 and the countersubstrate 20, and by irradiating the liquid crystal layer 30 with acertain amount of light or applying heat thereto to polymerize thepolymerizable monomer. At this time, the polymerization is performed ina state where no voltage or a voltage less than the threshold is appliedto the liquid crystal layer 30 so as to form the PS layers 17 and 27that retain the initial alignment of the liquid crystal molecules. As aresult, the PS layers 17 and 27 each having higher alignment stabilitycan be achieved. A polymerization initiator may be added to the liquidcrystal composition, if necessary.

The liquid crystal display panel according to Embodiment 1 includes theTFT substrate 10, the liquid crystal layer 30, and the counter substrate20, which are laminated in the stated order from a back surface to anobservation surface side of the liquid crystal display device. Linearpolarizing plates 18 and 28 are disposed on the back surface side of theTFT substrate 10 and the observation surface side of the countersubstrate 20, respectively. Each of these linear polarizing plates 18and 28 may further be provided with a retarder, and may be a circularlypolarizing plate.

The liquid crystal display panel according to Embodiment 1 may include acolor-filter-on-array structure in which a color filter is disposed onthe TFT substrate 10 instead of on the counter substrate. The liquidcrystal display panel according to Embodiment 1 may also be a monochromedisplay device or a field sequential color device. In that case, thecolor filter is unnecessary.

The liquid crystal layer 30 is filled with a liquid crystal materialhaving a property of being aligned in a specific direction when acertain voltage is applied thereto. The alignment of liquid crystalmolecules in the liquid crystal layer 30 is controlled by theapplication of a threshold or higher voltage.

FIG. 6 is a planar schematic diagram showing a slit electrode accordingto Embodiment 1. As shown in FIG. 6, the slit portion of the slitelectrode 12 is formed such that the linear portions of the electrodeare extended substantially in parallel to each other and linearly. InFIG. 6, the polarization direction of irradiated ultraviolet light istilted 10° from the longitudinal direction of the electrode. Thedouble-headed arrow in FIG. 6 shows the polarization direction ofirradiation (in the case where negative liquid crystal molecules areused). The pixel according to Embodiment 1 has two domains, so that theslit is bent, as shown in FIG. 6. Indium tin oxide (ITO) was used as anelectrode material. Other known materials such as indium zinc oxide(IZO) can also be used.

Hereinafter, an example of actual production of the liquid crystaldisplay panel according to Embodiment 1 is described.

A 10-inch IGZO-TFT substrate including an FFS structure, and a CFsubstrate as a counter substrate were provided, and a polyvinylcinnamate solution was applied to both substrates by spin coating. TheIGZO-TFT substrate is a thin film transistor array substrate in whichindium gallium zinc complex oxide is used as a semiconductor. Inaddition, the width L of the slit electrode on the upper layer was 3 μm,and the distance between the linear portions of the electrode (slitwidth S) was 5 μm (L/S=3 μm/5 μm). The polyvinyl cinnamate solution wasprepared by dissolving 3% by weight of polyvinyl cinnamate in a solventobtained by mixing N-methyl-2-pyrrolidone and ethylene glycol monobutylether in equal amount. After application by spin coating, the alignmentfilm was temporarily dried at 80° C. for 3 minutes, and then baked at200° C. for 40 minutes while purging nitrogen gas. The alignment film(the uppermost layer, i.e., the layer closest to the liquid crystallayer) on the transparent electrode on the TFT substrate has a filmthickness of 45 nm in the active area. The alignment film on the CFsubstrate has a film thickness of 50 nm in the active area. The diameterof each photospacer formed on the CF substrate is 17 μm, as measured onthe bottom (base).

These substrates were irradiated with linearly polarized ultravioletlight having a wavelength of 313 nm and an intensity of 5 J/cm² from thenormal direction of the substrates for liquid crystal alignmenttreatment. As described above, the angle formed between the lineconnecting two nearest adjacent photospacers (the photospacer 29 a andthe photospacer 29 b) and the polarization direction (not shown) is 90°.In other words, the angle formed between the line connecting thephotospacer 29 a and the photospacer 29 b and the liquid crystalalignment direction 32 is 0°, and the line connecting the two nearestadjacent photospacers is parallel to the liquid crystal alignmentdirection.

Next, a thermosetting seal (HC1413FP: manufactured by Mitsui Chemicals,Inc.) was printed on the TFT substrate by using a screen plate. Theheight of each photospacer is set such that the liquid crystal layer inthe active area has a thickness of 3.5 μm. These two kinds of substrateswere bonded to each other such that the polarization direction ofirradiated ultraviolet light is consistent between the substrates. Next,the bonded substrates were heated at 130° C. for 60 minutes in anitrogen-purged furnace while applying a pressure of 0.5 kgf/cm²thereto, and the seal was thus cured.

Liquid crystal was injected under vacuum into a panel produced byabove-described method. In the present embodiment, a mixture, which wasobtained by adding 5% by weight oftrans-4-propyl-4′-vinyl-1,1′-bicyclohexane to 100% by weight of MLC-6610(manufactured by Merck KGaA) and by further adding 1% by weight ofbiphenyl-4,4′-diyl bis(2-methylacrylate) as a polymerizable additive (amaterial (monomer) of the PS layer) thereto, was used as the liquidcrystal. An inlet of a cell through which the liquid crystal wasinjected was sealed with an epoxy adhesive (ARALDITE AR-530,manufactured by NICHIBAN Co., Ltd.). At this time, the electrodes wereshort-circuited and the charge removing on the glass surface wasperformed so that the liquid crystal alignment would not be disturbed byan external electric field. Next, in order to remove the liquid crystalflow alignment and to simulate the curing of the seal in the one dropfill (ODF) process during mass production, the panel was heated at 130°C. for 40 minutes to transform liquid crystal into the isotropic phasefor realignment treatment. As a result, a liquid crystal display panelof an FFS mode in which the liquid crystal molecules were uniaxiallyaligned in a direction perpendicular to the polarization direction ofultraviolet light with which the alignment films were irradiated wasobtained. All the processes were performed under yellow fluorescentlight to prevent the liquid crystal panel from being exposed toultraviolet light emitted from a fluorescent lamp. Subsequently, inorder to perform PS treatment on this panel, the panel was irradiatedwith ultraviolet light (1.5 J/cm²) by using a black light (FHF32BLB,manufactured by TOSHIBA Corporation). As a result, biphenyl-4,4′-diylbis(2-methylacrylate) was polymerized. This liquid crystal panel wasobserved for the presence of string-like defects under a microscope.Only about 40 string-like defects were present, i.e., the number sharplydecreased, compared to the later-described Comparative Example 1.

The liquid crystal display device including the above-described liquidcrystal display panel of Embodiment 1 may further appropriately includeother members (for example, light source such as a back light) that areincluded in common liquid crystal display devices. The liquid crystaldisplay device of Embodiment 1 is suitably applicable to TV panels,digital signage, medical monitors, electronic books, PC monitors,portable terminal panels, and the like. Liquid crystal display panelsaccording to the later-described embodiments are also applicable in thesame manner.

The type of the liquid crystal display device according to Embodiment 1may be any of transmissive type, reflective type, andreflective-transmissive combination type. In the case of thetransmissive or reflective-transmissive combination type, the liquidcrystal display device of Embodiment 1 includes a back light. The backlight is disposed on the back surface side of the liquid crystal cellsuch that the light is transmitted through the TFT substrate 10, theliquid crystal layer 30, and the counter substrate 20 in the statedorder. In the case of the refractive or reflective-transmissivecombination type, the TFT substrate 10 includes a reflector to reflectoutside light. In addition, the polarizing plate on the countersubstrate 20 must be a circularly polarizing plate at least in the areawhere the reflected light is used as display light.

The liquid crystal display device according to Embodiment 1 isdisassembled, and the collected liquid crystal is enclosed in a cell. Inthis way, the elastic constant can be measured by using EC-1manufactured by TOYO Corporation. The measurement temperature is 20° C.In addition, a chemical analysis using gas chromatograph massspectrometry (GC-MS), time-of-flight secondary ion mass spectrometry(TOF-SIMS), and the like can be carried out to analyze the components ofa horizontal photo-alignment film and the components in the polymerlayer. Furthermore, the cross-sectional shape of a liquid crystal cellcontaining an alignment film and a PS layer can be confirmed bymicroscopic observation using a scanning transmission electronmicroscope (STEM), a scanning electron microscope (SEM), or the like.

Modified Example of Embodiment 1

FIG. 7 is a cross-sectional schematic diagram showing an embodiment of aliquid crystal display panel according to a modified example ofEmbodiment 1. FIG. 8 is a planar schematic diagram showing a pair ofcombteeth electrodes according to a modified example of Embodiment 1.The modified example of Embodiment 1 relates to a liquid crystal displaypanel of an IPS mode.

In FIG. 7, a TFT substrate 110 includes an insulating transparentsubstrate 115 formed of glass or the like, and further includes signalelectrodes 111 (signal electrodes), common electrodes 112, variouswiring, TFTs, and the like, which are formed on the transparentsubstrate 115. For example, in the case of a liquid crystal displaypanel of an IPS mode as in the modified example of Embodiment 1, pairsof combteeth electrodes 113 (consisting of the signal electrodes 111 andthe common electrodes 112) are formed only in the TFT substrate 110, asshown in FIG. 7.

The pair of combteeth electrodes 113 is formed such that, as shown inFIG. 8, the signal electrode 111 and the common electrode 112 areextended substantially in parallel to each other and bent. Thereby, whenan electric field is applied, the electric field vector is substantiallyperpendicular to the length direction of the electrodes, and amulti-domain structure is thus formed, providing favorable viewing anglecharacteristic. The double-headed arrow in FIG. 8 indicates thepolarization direction of irradiation (in the case of using negativetype liquid crystal molecules), in the same manner as described abovefor FIG. 6.

Other elements of the modified example of Embodiment 1 are the same asthose of Embodiment 1 described above. The advantageous effects of thepresent invention can also be achieved by such a liquid crystal displaypanel of an IPS mode. The present invention is also applicable to liquidcrystal display panels of other modes such as FLC and AFLC modes.

Embodiment 2

Embodiment 2 is the same as Embodiment 1, except that an angle formedbetween a line connecting two nearest adjacent photospacers and analignment direction of liquid crystal molecules at a voltage lower thana threshold voltage in the liquid crystal layer is 20°. This liquidcrystal panel was observed for the presence of string-like defects undera microscope. Only about 50 string-like defects were present, i.e., thenumber sharply decreased.

Embodiment 3

Embodiment 3 is the same as Embodiment 1, except that the diameter ofthe bottom (base) of each photospacer formed on the CF substrate waschanged to 14 μm. This liquid crystal panel was observed for thepresence of string-like defects under a microscope. Only about 20string-like defects were present.

Embodiment 4

Embodiment 4 is the same as Embodiment 1, except that the diameter ofthe bottom (base) of each photospacer formed on the CF substrate waschanged to 12 μm. This liquid crystal panel was observed for thepresence of string-like defects under a microscope. Only about fivestring-like defects were present. The results of Embodiments 3 and 4indicate that the diameter of each photospacer formed on the CFsubstrate as measured on the bottom (base) is preferably 14 μm or lessand more preferably 12 μm or less.

In the liquid crystal display devices of a PS-FFS (PS-treated FFS) modeof Embodiments 1 to 4 described above and the liquid crystal displaydevice of a PS-IPS (PS-treated IPS) mode of the modified example ofEmbodiment 1 described above, alignment of the liquid crystal moleculesby photo-alignment is more preferred than alignment thereof by rubbingbecause it can suppress the alignment unevenness and the generation ofdust. Photo-alignment is further preferred because it does not cause apretilt in liquid crystal, unlike rubbing, and provides good viewingangle characteristic. However, because the horizontal photo-alignmentfilm generally has a weak alignment regulating force, severe imagesticking is observed, which makes mass production difficult. (Herein,the horizontal photo-alignment film refers to the horizontal alignmentfilm that is also a photo-alignment film. It aligns liquid crystalmolecules substantially horizontally to the substrate; contains afunctional group that causes photoisomerization, photodimerization,photodissociation in molecules of the alignment film by lightirradiation; and is also capable of aligning the liquid crystalmolecules by polarized light irradiation.) Thus, the present inventorssolved this problem through PS (polymer sustained) treatment. However,the horizontal photo-alignment film, in particular, can be a factor thatcauses string-like defects because of its weak alignment regulatingforce. The present inventors successfully solved this problem byselecting a suitable direction of liquid crystal alignment. Thus, it isconsidered that the present invention also provides a very simple methodof achieving a photo-aligned IPS mode.

In the actual usage, in the case of an application that involvesexposure to visible light (for example, in the case of a liquid crystalTV), the use of visible light for alignment treatment of thephoto-alignment film should be avoided as much as possible. However, inthe embodiments described above, the alignment film surface is coveredby the PS layer as a result of PS treatment, and the alignment is thusimmobilized. This is advantageous in that a material whose sensitivitywavelength includes a visible light wavelength range may be used as thematerial of the photo-alignment film.

Conventionally, an ultraviolet absorption layer needed to be provided inorder to prevent exposure to weak ultraviolet light from a back lightand the surrounding environment, even when the sensitivity wavelength ofthe material of the photo-alignment film included an ultravioletwavelength range. In this respect, the present invention providesanother advantage in that the PS process eliminates the need to providean ultraviolet absorption layer.

When PS treatment is performed by using ultraviolet light, the voltageholding ratio (VHR) may decrease due to irradiation of liquid crystalwith ultraviolet light. However, efficient PS treatment as in theembodiments described above can reduce the ultraviolet irradiation time,and a decrease in the voltage holding ratio can thus be avoided.

In addition, the PS exposure dose (time) can be decreased because ofreduced image sticking. In the production of liquid crystal panels, adecrease in the exposure dose (time) results in an increase in thethroughput. Furthermore, because the irradiation apparatus can be madesmaller, it leads to a reduction in the capital investment.

The irradiation of linearly polarized ultraviolet light forphoto-alignment treatment in the above-described embodiments isperformed before the bonding of the pair of substrates. However, thepair of substrates maybe bonded first, and then photo-alignmenttreatment may be performed from the outside of the liquid crystal cell.It does not matter whether photo-alignment treatment is performed beforeor after liquid crystal filling; however, when photo-alignment treatmentby irradiation of linearly polarized ultraviolet light is performedafter liquid crystal filling, it makes it possible to simultaneouslyperform photo-alignment treatment and the PS process, whichadvantageously reduces the process time.

Comparative Example 1

FIG. 9 is a planar schematic diagram showing spacer arrangement andalignment of liquid crystal molecules in a liquid crystal display panelaccording to Comparative Embodiment 1. In Comparative Example 1, thephotospacers are arranged at regular intervals of 150 μm in thelongitudinal direction and 50 μm in the transverse direction. Thephotospacers are regularly located at the intersections of the grid inwhich the vertical length of the unit cell is 150 μm and the horizontallength of the unit cell is 50 μm. Herein, the sections partitioned bythe grid-like black matrix may be pixels.

An angle formed between a line connecting spacers (a photospacer 229 aand a photospacer 229 b) with a shorter inter-spacer distance and theliquid crystal alignment direction 32 is 90°. The line connecting thetwo nearest adjacent photospacers is perpendicular to the liquid crystalalignment direction. As described above, in a plan view of the mainsurface of the pair of substrates, the liquid crystal display panelincludes the spacers that are arranged such that the inter-spacerdistance between the adjacent spacers in the longitudinal direction isdifferent from that in the transverse direction; and the angle formedbetween the line connecting the spacers with a shorter inter-spacerdistance than the other inter-spacer distance and the alignmentdirection of the liquid crystal molecules at a voltage lower than athreshold voltage in the liquid crystal layer is substantially 90°.Other elements of Comparative Example 1 are the same as those ofEmbodiment 1 described above. This liquid crystal panel was observed forthe presence of string-like defects under a microscope, and 200 or morestring-like defects were observed.

FIG. 10 is a view showing alignment and alignment singularities ofliquid crystal molecules in a liquid crystal display panel according toComparative Embodiment 1. FIG. 11 is an image showing a display area ofa liquid crystal display panel according to Comparative Example 1.

In Comparative Example 1, alignment singularities 236 are present at thetwelve o'clock position (top side) and the six o'clock position (bottomside) of a photospacer as shown in FIG. 10. When a string-like defect234 occurs, such a string-like defect 234 is an alignment defect, andalways has the alignment singularity 236 at each end thereof. Thus, whenthe string-like defect 234 occurs, it is more likely to project to theoutside of BM (the outside of a region connecting the shortest distancebetween nearest adjacent spacers) in Comparative Example 1 than inEmbodiment 1. In addition, the string-like defect 234 is considered tobe more stable when it is located along the alignment direction ofliquid crystal, and thus, the string-like defect 234 in ComparativeExample 1 tends to form a curvature and project to the outside of BM.These are considered to be the reasons why more string-like defects wereobserved in Comparative Example 1.

Hereinafter, a monomer that can be suitably used in the presentembodiment is described in detail. The monomer used for the formation ofthe polymer layer of the present invention can be confirmed byconfirming the molecular structure of the monomer unit in the polymerlayer of the present invention.

The polymer layer is preferably a polymerized product of a monomerpolymerizable by light irradiation. In particular, the polymer layer ispreferably formed by polymerization of a monomer polymerizable byultraviolet irradiation.

The polymer layer is also preferably formed by polymerization of amonomer including a monofunctional or polyfunctional polymerizable groupincluding at least one kind of ring structure. Examples of the monomerinclude compounds represented by the following chemical formula (1):

[Chem. 1]

P¹—S_(p) ¹—R²-A¹-(Z-A²)_(m)-R¹  (1)

In the formula, R¹ represents a —R²-Sp¹-P¹ group, a hydrogen atom, ahalogen atom, a —CN group, an —NO₂ group, an —NCO group, an —NCS group,an —OCN group, an —SCN group, an —SF₅ group, or a C1 to C12 linear orbranched alkyl group. P¹ represents a polymerizable group. Sp¹represents a C1 to C6 linear, branched, or cyclic alkylene group oralkyleneoxy group, or a direct bond. A hydrogen atom in R¹ may besubstituted with a fluorine atom or a chlorine atom. A —CH₂— group in R¹may be substituted with an —O— group, an —S— group, an —NH— group, a—CO— group, a —COO— group, an —OCO— group, an —O—COO— group, an —OCH₂—group, a —CH₂O— group, an —SCH₂— group, a —CH₂S— group, an —N(CH₃)—group, an —N(C₂H₅)— group, an —N(C₃H₇)— group, an —N(C₄H₉)— group, a—CF₂O— group, an —OCF₂— group, a —CF₂S— group, an —SCF₂— group, an—N(CF₃)— group, a —CH₂CH₂— group, a —CF₂CH₂— group, a —CH₂CF₂— group, a—CF₂CF₂— group, a —CH═CH— group, a —CF═CF— group, a —C≡C— group, a—CH═CH—COO— group, or an —OCO—CH═CH— group, as long as an oxygen atomand a sulfur atom are not adjacent to each other. R² represents an —O—group, an —S— group, an —NH— group, a —CO— group, a —COO— group, an—OCO— group, an —O—COO— group, an —OCH₂— group, a —CH₂O— group, an—SCH₂— group, a —CH₂S— group, an —N(CH₃)— group, an —N(C₂H₅)— group, an—N(C₃H₇)— group, an —N(C₄H₉)— group, a —CF₂O— group, an —OCF₂— group, a—CF₂S— group, an —SCF₂— group, an —N(CF₃)— group, a —CH₂CH₂— group, a—CF₂CH₂— group, a —CH₂CF₂— group, a —CF₂CF₂— group, a —CH═CH— group, a—CF═CF— group, a —C≡C— group, a —CH═CH—COO— group, an —OCO—CH═CH— group,or a direct bond. A¹ and A² are the same or different, and eachrepresents a 1,2-phenylene group, a 1,3-phenylene group, a 1,4-phenylenegroup, a naphthalene-1,4-diyl group, a naphthalene-1,5-diyl group, anaphthalene-2, 6-diyl group, a 1,4-cyclohexylene group, a1,4-cyclohexenylene group, a 1,4-bicyclo[2.2.2]octylene group, apiperidine-1,4-diyl group, a naphthalene-2,6-diyl group, adecahydronaphthalene-2,6-diyl group, a1,2,3,4-tetrahydronaphthalene-2,6-diyl group, an indane-1,3-diyl group,an indane-1,5-diyl group, an indane-2,5-diyl group, aphenanthrene-1,6-diyl group, a phenanthrene-1,8-diyl group, aphenanthrene-2,7-diyl group, a phenanthrene-3,6-diyl group, ananthracene-1,5-diyl group, an anthracene-1,8-diyl group, ananthracene-2,6-diyl group, or an anthracene-2,7-diyl group. —CH₂— groupsin A¹ and A² each may be substituted with an —O— group or an —S— group,as long as they are not adjacent to each other. Hydrogen atoms in A¹ andA² each may be substituted with a fluorine atom, a chlorine atom, a —CNgroup, or a C1 to C6 alkyl, alkoxy, alkyl carbonyl, alkoxy carbonyl, oralkyl carbonyloxy group. Each Z are the same or different, andrepresents an —O— group, an —S— group, an —NH— group, a —CO— group, a—COO— group, an —OCO— group, an —O—COO— group, an —OCH₂— group, a —CH₂O—group, an —SCH₂— group, a —CH₂S— group, an —N(CH₃)— group, an —N(C₂H₅)—group, an —N(C₃H₇)— group, an —N(C₄H₉)— group, a —CF₂O— group, an —OCF₂—group, a —CF₂S— group, an —SCF₂— group, an —N(CF₃)— group, a —CH₂CH₂—group, a —CF₂CH₂— group, a —CH₂CF₂— group, a —CF₂CF₂— group, a —CH═CH—group, a —CF═CF— group, a —C≡C— group, a —CH═CH—COO group, an—OCO—CH═CH— group, or a direct bond; and m is 0, 1, or 2.

More specific examples thereof include any of compounds represented bythe following chemical formulae (2-1) to (2-5):

In each formula, each P¹ are the same or different, and each representsa polymerizable group.

Examples of P¹ above include an acryloyloxy group, a methacryloyloxygroup, a vinyl group, a vinyloxy group, an acryloylamino group, and amethacryloylamino group. Herein, hydrogen atoms in benzene rings andfused rings in the compounds represented by the above chemical formulae(2-1) to (2-5) may be partially or fully substituted with halogen atoms,or C1 to C12 alkyl or alkoxy groups. In addition, hydrogen atoms inalkyl and alkoxy groups may be partially or fully substituted withhalogen atoms. Further, the bonding positions of P¹ to the benzene ringsand the fused rings are not limited to the ones shown.

The polymer layer of the present embodiment may be a polymerized productof a monomer polymerizable by visible light irradiation.

Monomers for forming the polymer layer include two or more types ofmonomers. The monomer polymerizable by visible light irradiation may bea monomer that polymerizes another monomer. The monomer that polymerizesanother monomer refers to, for example, a monomer that undergoes achemical reaction upon visible light irradiation; initiates and promotespolymerization of another monomer that does not polymerize by itself byvisible light irradiation; and polymerizes itself, while the wavelengthrange that induces reaction is different depending on the molecularstructure. Owing to the monomer that polymerizes another monomer, alarge number of existing monomers that do not polymerize by lightirradiation (such as visible light) can be used as materials of thepolymer layer. Examples of the monomer that polymerizes another monomerinclude a monomer including a structure that generates a radical byvisible light irradiation.

Examples of the monomer that polymerizes another monomer includecompounds represented by the following chemical formula (3):

In the formula, A³ and A⁴ are the same or different, and each representsa benzene ring, a biphenyl ring, or a C1 to C12 linear or branched alkylor alkenyl group. At least one of A³ and A⁴ includes an -Sp²-P² group. Ahydrogen atom in A³ and A⁴ each may be substituted with an -Sp²-P²group, a halogen atom, a —CN group, an —NO₂ group, an —NCO group, an—NCS group, an —OCN group, an —SCN group, an —SF₅ group, or a C1 to C12linear or branched alkyl, alkenyl, or aralkyl group. Two adjacenthydrogen atoms in A³ and A⁴ each may be substituted with a C1 to C12linear or branched alkylene or alkenylene group to form a cyclicstructure. A hydrogen atom in an alkyl, alkenyl, alkylene, alkenylene,or aralkyl group in A³ and A⁴ each may be substituted with an -Sp²-P²group. A —CH₂— group in an alkyl, alkenyl, alkylene, alkenylene, oraralkyl group in A³ and A⁴ each may be substituted with an —O— group, an—S— group, an —NH— group, a —CO— group, a —COO— group, an —OCO— group,an —O—COO— group, an —OCH₂— group, a —CH₂O— group, an —SCH₂— group, a—CH₂S— group, an —N(CH₃)— group, an —N(C₂H₅)— group, an —N(C₃H₇)— group,an —N(C₄H₉)— group, a —CF₂O— group, an —OCF₂— group, a —CF₂S— group, an—SCF₂— group, an —N(CF₃)— group, a —CH₂CH₂— group, a —CF₂CH₂— group, a—CH₂CF₂— group, a —CF₂CF₂— group, a —CH═CH— group, a —CF═CF— group, a—C≡C— group, a —CH═CH—COO— group, or an —OCO—CH═CH— group, as long as anoxygen atom, a sulfur atom, and a nitrogen atom are not adjacent to oneanother. P² represents a polymerizable group. Sp² represents a C1 to C6linear, branched, or cyclic alkylene or alkyleneoxy group, or a directbond; and n is 1 or 2. A dotted line connecting A³ with Y and a dottedline connecting A⁴ with Y indicate that a Y-mediated bond may be presentbetween A³ and A⁴. Y represents a —CH₂— group, a —CH₂CH₂— group, a—CH═CH— group, an —O— group, an —S— group, an —NH— group, an —N(CH₃)—group, an —N(C₂H₅)— group, an —N(C₃H₇)— group, an —N(C₄H₉)— group, an—OCH₂— group, a —CH₂O— group, an —SCH₂— group, or a —CH₂S— group, or adirect bond.

More specific examples thereof include any of compounds represented bythe following chemical formulae (4-1) to (4-8):

In the formula, R³ and R⁴ are the same or different, and each representsan -Sp²-P² group, a hydrogen atom, a halogen atom, a —CN group, an —NO₂group, an —NCO group, an —NCS group, an —OCN group, an —SCN group, an—SF₅ group, or a C1 to C12 linear or branched alkyl, aralkyl, or phenylgroup. At least one of R³ and R⁴ includes an -Sp²-P² group. P²represents a polymerizable group. Sp² represents a C1 to C6 linear,branched, or cyclic alkylene or alkyleneoxy group, or a direct bond.When at least one of R³ and R⁴ represents a C1 to C12 linear or branchedalkyl, aralkyl, or phenyl group, a hydrogen atom in at least one of R³and R⁴ above may be substituted with a fluorine atom, a chlorine atom,or an -Sp²-P² group. A —CH₂— group in R³ and R⁴ each may be substitutedwith an —O— group, an —S— group, an —NH— group, a —CO— group, a —COO—group, an —OCO— group, an —O—COO— group, an —OCH₂— group, a —CH₂O—group, an —SCH₂— group, a —CH₂S— group, an —N(CH₃)— group, an —N(C₂H₅)—group, an —N(C₃H₇)— group, an —N(C₄H₉)— group, a —CF₂O— group, an —OCF₂—group, a —CF₂S— group, an —SCF₂— group, an —N(CF₃)— group, a —CH₂CH₂—group, a —CF₂CH₂— group, a —CH₂CF₂— group, a —CF₂CF₂— group, a —CH═CH—group, a —CF═CF— group, a —C≡C— group, a —CH═CH—COO— group, or an—OCO—CH═CH— group, as long as an oxygen atom, a sulfur atom, and anitrogen atom are not adjacent to one another.

Examples of P² above include an acryloyloxy group, a methacryloyloxygroup, a vinyl group, a vinyloxy group, an acryloylamino group, and amethacryloylamino group. Herein, hydrogen atoms in benzene rings in thecompounds represented by the above chemical formulae (4-1) to (4-8) maybe partially or fully substituted with halogen atoms or C1 to C12 alkylor alkoxy groups. In addition, hydrogen atoms in alkyl and alkoxy groupsmay be partially or fully substituted with halogen atoms. Further, thebonding positions of R³ and R⁴ to the benzene rings are not limited tothe ones shown.

The monomers for forming the polymer layer (for example, the compoundsrepresented by the above chemical formulae (2-1) to (2-5), and thecompounds represented by the above chemical formulae (4-1) to (4-8))preferably include two or more polymerizable groups. For example,monomers including two polymerizable groups are preferred.

In the present invention, the above-described monomers may be added toliquid crystal without using a conventional polymerization initiator.This results in a significant improvement in electric properties becausethere is no residual polymerization initiator that can be an impurity inthe liquid crystal layer. In other words, a polymerization initiator forthe monomers can be substantially absent in the liquid crystal layerwhen the monomers are polymerized.

In the present embodiment, for example, a biphenyl-based bifunctionalmethacrylate monomer represented by the following chemical formula (5)may be used.

In this case, the formation of a polymer can be ensured without mixing aphotopolymerization initiator. The radical generation processrepresented by the following formulae (6-1) and (6-2) is considered tobe induced by light irradiation.

In addition, the present of a methacrylate group helps the monomer toform a polymer by radical polymerization.

Monomers that dissolve in liquid crystal are preferred as the monomers.Rod-like molecules are preferred as the monomers. Examples thereof mayinclude naphthalene-based, phenanthrene-based, and anthracene-basedmonomers, in addition to the biphenyl-based monomer. In addition,hydrogen atoms therein may be partially or fully substituted withhalogen atoms, alkyl groups, or alkoxy groups (hydrogen atoms in thesegroups may be partially or fully substituted with halogen atoms).

Examples of polymerizable groups may also include an acryloyloxy group,a vinyloxy group, an acryloylamino group, and a methacryloylamino group,in addition to the methacryloyloxy group. These monomers can generateradicals by light having a wavelength ranging from about 300 to 380 nm.

In addition to the above monomers, monomers such as acrylate anddiacrylate having no photopolymerization initiating function may bemixed. The photopolymerization reaction rate can be adjusted with thesemonomers.

In addition, in the present embodiment, a mixture of a monomerrepresented by the following chemical formula (7A) and a monomerrepresented by the following chemical formula (7B) can also be used.

In this case, the PS process may be performed with visible lightirradiation. This reduces damage to the liquid crystal and thephoto-alignment film. Other examples of monomers that can be usedinclude benzoin ether-based, acetophenone-based, benzil ketal-based, andketone-based monomers, which generate radicals by photofragmentation andhydrogen abstraction. A polymerizable group must be attached to thesemonomers.

Examples of the polymerizable group include an acryloyloxy group, avinyloxy group, an acryloylamino group, and a methacryloylamino group,in addition to the methacryloyloxy group.

In addition, in the present embodiment, a polyimide including acyclobutane skeleton may be used as the main chain of a polymer of analignment film material.

Next, a preferred embodiment of the liquid crystal layer in the liquidcrystal display device of the present embodiment will be described. Theliquid crystal layer preferably contains liquid crystal moleculesincluding, in a molecular structure thereof, a multiple bond other thanconjugated double bonds of a benzene ring. The liquid crystal moleculesmay have either positive anisotropy of dielectric constant (positivetype) or negative anisotropy of dielectric constant (negative type). Theliquid crystal molecules are preferably nematic liquid crystal moleculeshaving a high symmetric property in the liquid crystal layer.

The multiple bond does not include conjugated double bonds of a benzenering because the benzene ring has low reactivity. However, as long asthe liquid crystal molecule includes, as an essential bond, a multiplebond other than conjugated double bonds of a benzene ring, the liquidcrystal molecules of the present embodiment may include conjugateddouble bonds of a benzene ring: the conjugated double bonds does nothave to be particularly excluded. In addition, in the presentembodiment, the liquid crystal molecules contained in the liquid crystallayer may be a mixture of plural kinds thereof. A liquid crystalmaterial may be a mixture of plural kinds of liquid crystal molecules inorder to secure the reliability, to improve the response speed, and toadjust the liquid crystal phase temperature range, elastic constant,anisotropy of dielectric constant, and refractive index anisotropy.

The multiple bond is preferably a double bond, and it is more preferredthat the double bond be present in an ester group or an alkenyl group.For example, it is preferred that the double bond is present in analkenyl group. The double bond has a higher reactivity than a triplebond. The multiple bond may be a triple bond, and in that case, thetriple bond is preferably present in a cyano group. Further, each liquidcrystal molecule preferably includes two or more kinds of multiplebonds.

Each liquid crystal molecule preferably contains at least one molecularstructure selected from the group consisting of structures representedby the following formulae (8-1) to (8-6). Among these, a molecularstructure represented by the following formula (8-4) is particularlypreferred.

Lastly, the bottom diameter (diameter as measured on the bottom (base))of the PS as defined herein is described. FIG. 12 is a planar schematicdiagram showing a grid-like black matrix BM and photospacers 29 in thepresent embodiment. FIG. 13 is a cross-sectional schematic diagram ofFIG. 12. A flattening film 22 and the like are disposed on the blackmatrix BM; and an alignment film 26 d made from polyimide or the like isdisposed on the flattening film 22 and the like. The bottom diameter ofthe PS is the diameter of its surface on the alignment film 226 d, whichis opposite to the liquid crystal layer. It is expressed as “dB”.

Embodiment 5

In Embodiment 5, a cell was completed in the same manner as inEmbodiment 1, except for the below-described alignment film material andalignment treatment conditions.

A polyimide solution including a cyclobutane skeleton was used as analignment film material. The alignment film material was applied to thesubstrates and dried in the same manner as in Embodiment 1.

The surface of each substrate was irradiated with polarized ultravioletlight having a wavelength of 254 nm with an intensity of 500 mJ/cm² fromthe normal direction of each substrate for alignment treatment. As aresult, the alignment film material applied to the substrates causedphotodissociation, and horizontal alignment films were thus formed.

This liquid crystal panel was observed for the presence of string-likedefects under a microscope. Only one string-like defect was present.

Embodiment 6

Embodiment 6 is the same as Embodiment 1, except that the diameter ofthe bottom (base) of each photospacer formed on the CF substrate waschanged to 9 μm. This liquid crystal panel was observed for the presenceof string-like defects under a microscope. Only about two string-likedefects were observed.

Each of the embodiments described above may be suitably combined withoutdeparting from the scope of the present invention.

The present application claims priority to Patent Application No.2011-185045 filed in Japan on Aug. 26, 2011 under the Paris Conventionand provisions of national law in a designated State, the entirecontents of which are hereby incorporated by reference.

REFERENCE SIGNS LIST

-   10, 110: TFT substrate (array substrate)-   12: slit electrode-   13: insulation layer-   14: lower layer electrode-   15, 25, 115, 125: glass substrate-   16, 26, 116, 126: alignment film (horizontal photo-alignment film)-   17, 27, 117, 127: PS layer (polymer layer)-   18, 28, 118, 128: linear polarizing plate-   20, 120: counter substrate (CF substrate)-   29, 29 a, 29 b, 29 c, 29 d, 29 e, 29 f, 129, 229 a, 229 b, 229 c,    229 d,-   229 e, 229 f: spacer-   30, 130: liquid crystal layer-   32, 32 p, 132, 232: liquid crystal alignment direction-   34, 234: string-like defect-   111: signal electrode-   112: common electrode-   113: a pair of combteeth electrodes-   R: red pixel-   G: green pixel-   B: blue pixel

1. (canceled)
 2. A liquid crystal display panel comprising: a pair ofsubstrates; and a liquid crystal layer interposed between the pair ofsubstrates, wherein at least one of the pair of substrates includes analignment film and an electrode in the stated order from the liquidcrystal layer side, the alignment film aligns liquid crystal moleculeshorizontally to a main surface of the at least one of the pair ofsubstrates, the liquid crystal molecules in the liquid crystal layerhave negative anisotropy of dielectric constant, the liquid crystaldisplay panel includes multiple spacers between the pair of substrates,the spacers being arranged such that an inter-spacer distance betweenadjacent spacers in a longitudinal direction is different from aninter-spacer distance between adjacent spacers in a transverse directionin a plan view of the main surface of the pair of substrates, and anangle defined between a line connecting the spacers with a shorterinter-spacer distance than the other inter-spacer distance and analignment direction of the liquid crystal molecules at a voltage lowerthan a threshold voltage in the liquid crystal layer is 20° or smalleras seen in a plan view of the main surface of the at least one of thepair of substrates.
 3. The liquid crystal display panel according toclaim 2, wherein the line connecting the spacers with a shorterinter-spacer distance is parallel to the alignment direction of theliquid crystal molecules at a voltage lower than a threshold voltage inthe liquid crystal layer.
 4. The liquid crystal display panel accordingto claim 2, wherein the alignment film includes a photoactive material.5. The liquid crystal display panel according to claim 4, wherein thephotoactive material includes a cyclobutane skeleton in a repeatingunit.
 6. The liquid crystal display panel according to claim 2, whereinthe spacers are photospacers disposed on the at least one of the pair ofsubstrates and projecting toward the liquid crystal layer.
 7. The liquidcrystal display panel according to claim 6, wherein each of thephotospacers has a diameter of 14 μm or less as measured on its surfacein contact with the at least one of the pair of substrates.
 8. Theliquid crystal display panel according to claim 2, wherein an alignmentmode of the liquid crystal layer is in an IPS mode or an FFS mode. 9.The liquid crystal display panel according to claim 2, wherein theliquid crystal layer contains the liquid crystal molecules including, ina molecular structure thereof, a multiple bond other than conjugateddouble bonds of a benzene ring.
 10. The liquid crystal display panelaccording to claim 9, wherein the multiple bond is a double bond. 11.The liquid crystal display panel according to claim 10, wherein thedouble bond is present in an alkenyl group.